Trust has been consistently identified as an important enabling factor for joined-up government activity to generate strong, integrated and effective social policy. Despite this, there has been comparatively little detailed analysis of the complexities and dynamics involved. This paper provides a detailed examination of how trust is built, nurtured and, in some instances, lost during joined-up policy activity. It draws on interview and survey data that reveal the dynamics of relationships formed under the South Australian Health in All Policies initiative. The research extends the parameters of organisational analyses of trust. Previous typologies are mostly descriptive, with limited explanatory power, typically focusing on individuals and institutions separately rather than integrating these foci to consider how trust operates within whole systems. By integrating Giddens’ theoretical perspectives on trust with existing typologies, the paper generates understanding about how trust operates as a resource within non-traditional joined-up government working relationships, serving to bridge the gap between the known and unknown, and acting as a productive resource to stimulate action within government systems that are perceived to feature high levels of risk. A model is provided to explain the interrelated dynamics of trust building, maintenance, monitoring and repair.